use crate::{
	attrs::{parse_doc_attr, ContainerAttributes, FieldAttributes},
	util::ToLitStr
};
use proc_macro2::{Ident, Span};
use serde_derive_internals::attr::RenameRule;
use syn::{
	punctuated::Punctuated, spanned::Spanned as _, AngleBracketedGenericArguments, DataEnum, DataStruct, DataUnion, Fields,
	FieldsNamed, GenericArgument, LitStr, PathArguments, Type, TypePath
};
use syn_path::path;

pub(super) enum TypeOrInline {
	Type(Box<Type>),
	Inline(ParseData)
}

pub(super) struct ParseDataField {
	pub(super) name: LitStr,
	pub(super) doc: Vec<String>,
	pub(super) ty: TypeOrInline,
	pub(super) flatten: bool
}

#[allow(dead_code)]
pub(super) struct ParseData {
	pub(super) name: Option<LitStr>,
	pub(super) doc: Vec<String>,
	pub(super) ty: ParseDataType
}

pub(super) enum ParseDataType {
	Struct {
		fields: Vec<ParseDataField>,
		deny_unknown_fields: bool
	},
	Enum {
		variants: Vec<LitStr>
	},
	Alternatives {
		alts: Vec<TypeOrInline>
	},
	Unit
}

fn parse_named_fields(named_fields: &FieldsNamed, rename_all: Option<&LitStr>) -> syn::Result<Vec<ParseDataField>> {
	let mut fields: Vec<ParseDataField> = Vec::new();
	for f in &named_fields.named {
		// parse #[serde] and #[openapi] attributes
		let mut attrs = FieldAttributes::default();
		for attr in &f.attrs {
			if attr.path.is_ident("serde") {
				attrs.parse_from(attr, false)?;
			}
		}
		for attr in &f.attrs {
			if attr.path.is_ident("openapi") {
				attrs.parse_from(attr, true)?;
			}
		}

		// skip this field if desired
		if attrs.skip_serializing && attrs.skip_deserializing {
			continue;
		}

		// parse #[doc] attributes
		let mut doc = Vec::new();
		for attr in &f.attrs {
			if attr.path.is_ident("doc") {
				if let Some(lit) = parse_doc_attr(attr)? {
					doc.push(lit.value());
				}
			}
		}

		// get the name of the field
		let ident = f
			.ident
			.as_ref()
			.ok_or_else(|| syn::Error::new(f.span(), "#[derive(OpenapiType)] does not support fields without an ident"))?;
		let mut name = ident.to_lit_str();
		if let Some(rename) = attrs.rename {
			name = rename;
		} else if let Some(rename_all) = rename_all {
			let rule = RenameRule::from_str(&rename_all.value())
				.map_err(|_| syn::Error::new(rename_all.span(), "Unknown rename_all rule"))?;
			let rename = rule.apply_to_field(&name.value());
			name = LitStr::new(&rename, name.span());
		}

		// get the type of the field
		let mut ty = f.ty.to_owned();
		if attrs.nullable {
			let mut args = Punctuated::new();
			args.push(GenericArgument::Type(ty));
			let mut path = path!(::core::option::Option);
			let last = path.segments.last_mut().unwrap();
			last.arguments = PathArguments::AngleBracketed(AngleBracketedGenericArguments {
				colon2_token: None,
				lt_token: Default::default(),
				args,
				gt_token: Default::default()
			});
			ty = Type::Path(TypePath { qself: None, path })
		}

		fields.push(ParseDataField {
			name,
			doc,
			ty: TypeOrInline::Type(Box::new(ty)),
			flatten: attrs.flatten
		});
	}
	Ok(fields)
}

pub(super) fn parse_struct(ident: &Ident, strukt: &DataStruct, attrs: &ContainerAttributes) -> syn::Result<ParseData> {
	let name = attrs.rename.clone().unwrap_or_else(|| ident.to_lit_str());
	match &strukt.fields {
		Fields::Named(named_fields) => {
			let fields = parse_named_fields(named_fields, attrs.rename_all.as_ref())?;
			Ok(ParseData {
				name: Some(name),
				doc: attrs.doc.clone(),
				ty: ParseDataType::Struct {
					fields,
					deny_unknown_fields: attrs.deny_unknown_fields
				}
			})
		},
		Fields::Unnamed(unnamed_fields) => Err(syn::Error::new(
			unnamed_fields.span(),
			"#[derive(OpenapiType)] does not support tuple structs"
		)),
		Fields::Unit => Ok(ParseData {
			name: Some(name),
			doc: attrs.doc.clone(),
			ty: ParseDataType::Unit
		})
	}
}

pub(super) fn parse_enum(ident: &Ident, inum: &DataEnum, attrs: &ContainerAttributes) -> syn::Result<ParseData> {
	let mut strings: Vec<LitStr> = Vec::new();
	let mut types: Vec<(LitStr, TypeOrInline)> = Vec::new();

	for v in &inum.variants {
		let name = v.ident.to_lit_str();
		match &v.fields {
			Fields::Named(named_fields) => {
				let fields = parse_named_fields(named_fields, attrs.rename_all.as_ref())?;
				let struct_name = format!("{ident}::{}", name.value());
				// TODO add documentation here
				types.push((
					name,
					TypeOrInline::Inline(ParseData {
						name: Some(struct_name.to_lit_str()),
						doc: Vec::new(),
						ty: ParseDataType::Struct {
							fields,
							// serde seems to only allow this attribute on the outer
							// container, not on a per-variant basis
							deny_unknown_fields: attrs.deny_unknown_fields
						}
					})
				));
			},
			Fields::Unnamed(unnamed_fields) if unnamed_fields.unnamed.len() == 1 => {
				let ty = unnamed_fields.unnamed.first().unwrap().ty.clone();
				// TODO add documentation here
				types.push((name, TypeOrInline::Type(Box::new(ty))));
			},
			Fields::Unnamed(unnamed_fields) => {
				return Err(syn::Error::new(
					unnamed_fields.span(),
					"#[derive(OpenapiType)] does not support tuple variants"
				))
			},
			Fields::Unit => strings.push(name)
		}
	}

	let data_strings = if strings.is_empty() {
		None
	} else {
		Some(match (&attrs.tag, &attrs.content, attrs.untagged) {
			// externally tagged (default)
			(None, None, false) => ParseDataType::Enum { variants: strings },
			// internally tagged or adjacently tagged
			(Some(tag), _, false) => ParseDataType::Struct {
				fields: vec![ParseDataField {
					name: tag.clone(),
					doc: Vec::new(),
					ty: TypeOrInline::Inline(ParseData {
						name: None,
						doc: Vec::new(),
						ty: ParseDataType::Enum { variants: strings }
					}),
					flatten: false
				}],
				deny_unknown_fields: true
			},
			// untagged
			(None, None, true) => ParseDataType::Unit,
			// unknown
			_ => return Err(syn::Error::new(Span::call_site(), "Unknown enum representation"))
		})
	};

	let data_types = if types.is_empty() {
		None
	} else {
		Some(ParseData {
			name: Some(ident.to_lit_str()),
			doc: attrs.doc.clone(),
			ty: ParseDataType::Alternatives {
				alts: types
					.into_iter()
					.map(|(name, mut data)| {
						Ok(match (&attrs.tag, &attrs.content, attrs.untagged) {
							// externally tagged (default)
							(None, None, false) => {
								let struct_name = format!("{ident}::{}::ExtTagWrapper", name.value());
								TypeOrInline::Inline(ParseData {
									name: Some(struct_name.to_lit_str()),
									doc: Vec::new(),
									ty: ParseDataType::Struct {
										fields: vec![ParseDataField {
											name,
											doc: Vec::new(),
											ty: data,
											flatten: false
										}],
										deny_unknown_fields: true
									}
								})
							},
							// internally tagged
							(Some(tag), None, false) => {
								match &mut data {
									TypeOrInline::Inline(ParseData {
										ty: ParseDataType::Struct { fields, .. },
										..
									}) => fields.push(ParseDataField {
										name: tag.clone(),
										doc: Vec::new(),
										ty: TypeOrInline::Inline(ParseData {
											name: None,
											doc: Vec::new(),
											ty: ParseDataType::Enum { variants: vec![name] }
										}),
										flatten: false
									}),
									_ => return Err(syn::Error::new(
										tag.span(),
										"#[derive(OpenapiType)] does not support tuple variants on internally tagged enums"
									))
								};
								data
							},
							// adjacently tagged
							(Some(tag), Some(content), false) => {
								let struct_name = format!("{ident}::{}::AdjTagWrapper", name.value());
								TypeOrInline::Inline(ParseData {
									name: Some(struct_name.to_lit_str()),
									doc: Vec::new(),
									ty: ParseDataType::Struct {
										fields: vec![
											ParseDataField {
												name: tag.clone(),
												doc: Vec::new(),
												ty: TypeOrInline::Inline(ParseData {
													name: None,
													doc: Vec::new(),
													ty: ParseDataType::Enum { variants: vec![name] }
												}),
												flatten: false
											},
											ParseDataField {
												name: content.clone(),
												doc: Vec::new(),
												ty: data,
												flatten: false
											},
										],
										deny_unknown_fields: true
									}
								})
							},
							// untagged
							(None, None, true) => data,
							// unknown
							_ => return Err(syn::Error::new(Span::call_site(), "Unknown enum representation"))
						})
					})
					.collect::<syn::Result<Vec<_>>>()?
			}
		})
	};

	match (data_strings, data_types) {
		// only variants without fields
		(Some(ty), None) => Ok(ParseData {
			name: Some(ident.to_lit_str()),
			doc: attrs.doc.clone(),
			ty
		}),
		// only one variant with fields
		(
			None,
			Some(ParseData {
				ty: ParseDataType::Alternatives { mut alts },
				..
			})
		) if alts.len() == 1 && matches!(alts.first().unwrap(), TypeOrInline::Inline(..)) => Ok(ParseData {
			name: Some(ident.to_lit_str()),
			doc: attrs.doc.clone(),
			ty: match alts.remove(0) {
				TypeOrInline::Inline(data) => data.ty,
				_ => unreachable!() // if condition above
			}
		}),
		// only variants with fields
		(None, Some(data)) => Ok(data),
		// variants with and without fields
		(Some(data_strings), Some(mut data_types)) => {
			let alts = match &mut data_types.ty {
				ParseDataType::Alternatives { alts } => alts,
				// data_types always produces Alternatives
				_ => unreachable!()
			};
			alts.push(TypeOrInline::Inline(ParseData {
				name: None,
				doc: Vec::new(),
				ty: data_strings
			}));
			Ok(data_types)
		},
		// no variants
		(None, None) => Err(syn::Error::new(
			inum.brace_token.span,
			"#[derive(OpenapiType)] does not support enums with no variants"
		))
	}
}

pub(super) fn parse_union(union: &DataUnion) -> syn::Result<ParseData> {
	Err(syn::Error::new(
		union.union_token.span(),
		"#[derive(OpenapiType)] cannot be used on unions"
	))
}